PDCD1 and cancer: Programmed cell death ligand 1 (PD-L1) expressed in cancer cells is a functional ligand of programmed cell death 1 (PD-1) expressed in immune cells (Okazaki and Honjo, 2007), and high expression of PD-L1 could affect the evasion of host antitumor immunity of cancer cells, potentially abating the efficacy of anticancer therapies (Hino et al., 2010; Mittal et al., 2014).